Thus, given that such a multichannel reception system possesses as many reception channels as antennas of interest (i.e. an integer N), it therefore possesses as many spectral analyzers. The latter are used as measurers able to separate the signals frequency-wise through the spectral resolution that they possess.
These N spectral analyzers are all identical. Moreover, each possesses a restricted instantaneous band. There are two origins to this restriction:                the analyzers incorporate analog-digital converters having a limited analog band and a limited sampling frequency;        a likewise limited calculation capacity so as to absorb the stream of data in real time.        
On account of the use of these spectral analyzers, the reception system uses so-called superheterodyne reception channels. The latter make it possible, through a frequency transposition, to translate a frequency sub-band of the span of interest to a restricted frequency band associated with an intermediate frequency filter. This restricted band corresponds to the band of the spectral analyzer. This operation is repeated as necessary sub-band by sub-band so as to cover the whole of the span of interest.
As a variant, superheterodyne reception channels very generally employ double changes of frequency so as to cover a wide frequency band of interest while dealing with the problems of image frequencies. Stated otherwise, the translation of the frequency sub-band to the restricted band is very generally done in two steps.
It is noted that the translations performed are identical for all the superheterodyne reception channels of the reception system.
The instantaneous band of the reception system is that of the spectral analyzers incorporated in the reception system. It is therefore limited to a few hundred MHz. Given that the reception system must operate over a much larger span of interest (for example about ten GHz), this implies that certain transitory signals are not necessarily intercepted, and therefore that there is a probabilistic notion in the interception (cf. probability of interception).